Focusing of Gaussian beam passed under small angle to optical axis of uniaxial crystal

Abstract

We showed both experimentally and analytically, the effect of focusing of a Gaussian beam propagated under small angle φ with respect to the optical axis of a uniaxial crystal, on the generation of a bottle beam. At φ = 0° two foci that correspond to ordinary and extraordinary parts of a beam form a closed 3D structure of a bottle beam. At this point, the beam, in the foci points, has radially and azimuthally aligned polarizations. Increasing the value of φ leads to dramatic changes in the intensity and polarization structure of a bottle beam. Starting from the value of φ = ±2° the closed 3D symmetric structure of a bottle beam breaks down. At φ = ±5° both beams are focused at the same transverse plane, while its polarization evolves to x- and y-linear. With a further increase in angle φ two foci 'switch' their spatial positions and move further away.